BUSINESS SEGMENT INFORMATION (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Percentage of net revenues	100.00%	100.00%	100.00%	100.00%
Total net revenues	$ 2,786	$ 1,956	$ 6,435	$ 5,800
Total operating income	718	313	1,176	868
Non-operating income (expense), net	35	(43)	(50)	(120)
Income from continuing operations before income taxes and equity in earnings of equity method investees	753	270	1,126	748
Income tax expense	(177)	(62)	(269)	(175)
Equity in earnings of equity method investees, net of taxes	15	18	33	48
Income (loss) from continuing operations	591	226	890	621
Income from discontinued operations, net of taxes	0	0	0	20
Net income	591	226	890	641
Less: Net income attributable to noncontrolling interests	23	11	38	36
Net income attributable to Quest Diagnostics	$ 568	$ 215	$ 852	$ 605
DIS business
Segment Reporting Information [Line Items]
Percentage of net revenues	97.00%	96.00%	97.00%	96.00%
Total net revenues	$ 2,709	$ 1,877	$ 6,217	$ 5,561
Total operating income	$ 840	$ 345	$ 1,325	$ 963
DIS business | Minimum
Segment Reporting Information [Line Items]
Percentage of net revenues	95.00%	95.00%	95.00%	95.00%
All other operating segments
Segment Reporting Information [Line Items]
Total net revenues	$ 77	$ 79	$ 218	$ 239
Total operating income	16	10	29	31
General corporate activities
Segment Reporting Information [Line Items]
Total operating income	$ (138)	$ (42)	$ (178)	$ (126)